The present invention relates to a method of forming a mask pattern for a semiconductor device, and more particularly, to a method of forming a micro pattern.
In general, a semiconductor device, such as flash memory, includes thousands of micro patterns. The micro patterns are formed by means of a photolithography process. In order to form the micro patterns using the photolithography process, a photoresist is first coated on a subject film to be patterned. A common exposure process is then performed using a mask to change the solubility of the exposed photoresist film. A development process is performed to remove the portions whose solubility has been changed or not changed, thus forming a photoresist film pattern. An etch process using the photoresist film pattern as an etch mask is performed to remove the exposed portion of the subject film. The photoresist film pattern is stripped to form a subject film pattern.
In the photolithography process, two important issues are resolution and depth of focus (DOF). In the case of resolution of the exposure equipment, the shorter the wavelength of the light source and the larger the aperture setting (i.e., smaller opening), the higher the resolution. Accordingly, a greater number of micro patterns can be formed on the wafer. However, the wavelength of the light source and the aperture setting of the exposure equipment are limited, whereas the level of device integration continues to rapidly increase. A resolution enhancement technique (RET) for improving the resolution and the DOF by using several methods has been developed. The RET includes a double exposure technique (DET), a top-surface imaging process by silylation (TIPS) and the like.
The DET is a process by which the exposure and etch process are performed twice. The DET is advantageous in that it can form relatively micro patterns, but is disadvantageous in that overlay margin is weak and it is difficult to uniformly control the Critical Dimension (CD) between patterns.
The TIPS (top-surface imaging process by silylation) process is a process of performing shallow exposure so that diffusion reaction is selectively performed on exposed regions and non-exposed regions in order to form a latent image, and enabling silylation regions to serve as a mask and non-silylation regions to be developed. The TIPS process is advantageous compared with a general resist patterning process in that it has a very wide DOF compared with a single film resist in high resolutions, but is disadvantageous in that it has limitations in applying it to the next generation of even smaller micro patterns.